Double-frequency phase-angle relaying system



Oct. 10,1950 w, L s R 2,525,493

DOUBLE-FREQUENCY PHASE-ANGLE RELAYING-SYSTEM Filed Oct. 30, 1947 WITNESSES: INVENTOR M1 Herbert W Lensnek ATTORNEY Patented Oct. 10, 1950 DOUBLE-FREQUENCY PHASE-ANGLE RELAYING SYSTEM Herbert W. Lensner, East Orange, N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 30, 1947, Serial No. 783,161

4 Claims. (01.

My invention relates to phase-angle, or phasecomparing, carrier-current protective-relaying systems for protecting transmission-lines against faults.

The principal object of my inventionis to make such relaying-systems more reliable in their operation, when operating at two different carrier-frequencies, or to provide ,a reliable system which is operative at either one carrier-frequency or two carrier-frequencies.

For some years past, commercial use has been made of a phase-comparing protective-relaying system, the latest form of which is described and claimed in a joint application of S. L. Goldsborough, R. C. Check and myself, Serial No. 758,200, filed June 30, 1947. In such systems, a succession of bursts of carrier-current impulses are transmitted during alternate half-cycles of the line-current, whereas, during the intervening half-cycles, operating-current impulses are applied to a relay. The received carrier-current energy is used to prevent the effective application of the operating-current impulses to the relay during the times when carrier-current energy is being effectively received. The actual operatingcurrent which. is applied to the relay is supposed or assumed to be zero, under an ideal throughfault condition, that is, when the in-looking linecurrents at the two line-terminals are 180 out- When this 180 When such a phase-angle-comparing carriercurrent system is operated at two different car rier-current frequencies (the transmitter being tuned to one frequency, and the receiver being f,

tune-ii to another frequency), the relay-current does not drop to zero, under an ideal throughfault condition. On the contrary, cases have been observed, in which the relay-current under these conditions has been as much as 50 to 60% of the pickup value of the relay, thus creating a hazard of faulty operation'in systems in which the relay is given a particularly sensitive setting, or in cases where the relay-current may possibly reach the pickup value during a through-fault condition.

The reason for this difficulty is that the incoming half-cycles of carrier-current energy have an envelope which has an essentiallysquare-topped 60-cycle wave-form, which means infinite harmonics of,60 cycles in the received signal. The tuned circuits of the receiver will not pass the higher harmonics of cycles, and hence will not pass the square wave, with the result that the restraining voltag which is applied to the relay tube from the receiver will increase only gradually, at the beginning of each restraining-impulse half-cycle, The operating voltage, however, has a square (SO-cycle wave form, so that it increases suddenly to its final value, resulting in portions of a half-cycle during, which the application of the operating voltage is not offset by the restraining-voltage.

With single-frequency operation, that is, with both the transmitter and the receiver operating at the same carrier-frequency, the carrier-receiver theoretically receives essentially a continuous signal during ideal through-fault conditions, so that the restraint-voltage will be steady, and of a substantially constant value, so that therewill be no operating-voltage applie to the relay. I

An object of my present invention is to provide a delayed -build-up means, for delaying the building up of the operating impulses in the relay, without substantially delaying the decay of these operating-impulses, thus permitting the efiective operating-current of the relay to become zero during ideal through-fault conditions.

With the foregoing and other objects in view, my invention consists in the system, circuits, combinations, elements and methods of design and operation, which are hereinafter described and claimed, and illustrated in the accompanying drawing, the single figure of which is a much simplified diagrammatic view of circuits andapparatus illustrative of my invention in a preferred form of embodiment.

In the drawing, I have illustrated my invention as applied to one terminal of a line-section 1 of a 3-phase transmission-line, which is connected to a 3-phasestation-bus 2 by means of a circuit-breaker 3 having a trip-coil TC and an auxiliary make-contact 3a. I have shown only one terminal of the protectedline-section l, with the understanding that the other terminal is, or may be, a duplicate of the terminal equipment which is illustrated, except for a different carrier-current frequency, as will be subsequently noted.

I have illustrated a system using a bank of line-current transformers 4, which respond to the E-phase line-current in the protected linesection I, and I supply this current to any suitable network or filter, which is marked HOB, for deriving a single-phase alternating-current voltage which is applied to the primary winding of a saturable transformer ST. Any suitable network, such as HCB, may be utilized, for deriving a single-phase relaying current or voltage which is reasonably uniformly responsive to a plurality of kinds and severities of faults on whatever linephase a fault may occur. The secondary winding 6 of the saturable transformer ST is shunted by a voltage-limiting gas-filled tube GT-l, as described in the Harder Patent 2,183,646, granted December 19, 1939.

The secondary winding 6 is used to control two mechanical fault-detector relays FDI and FDZ having diverse sensitivity-settings, and also to control two alternately triggering gas-filled tubes VI and V2, as described in the copending joint application. The operating-coils of the two fault-detector relays FDI and FD2 are shown as being energized in series with each other, from the output-terminals of a rectifier-bridge RB, which is supplied with energy from the secondary winding 6 of the saturating transformer ST. The gas-filled tubes VI and V2 are controlled from the aforesaid secondary winding 6 by having the tube-grids GI and G2 energized, through resistors RI and R2, from two secondary windings II and I2 of an input-transformer IT, the primary of which is energized from the secondary winding 6 of the saturated transformer ST. The other two terminals of the secondary windings I I and I2 of the input-transformer IT are shown as being connected together, in a circuit I4 which is connected to an intermediate tapped-point of a cathode-circuit biasing-resistor R3, which is in the cathode-circuits of the gas-tubes VI and V2.

As shown in the drawing, one terminal of the cathode-circuit biasing-resistor R3 is connected to the negative bus of a, direct-current voltage-source for the tubes, while the other terminal of said resistor is connected to a conductor I5, which is used for several purposes. The circuit I is used to energize one terminal of cathodecircuit loading-resistor R4, the other terminal of which is connected to the cathode-terminal 2| of the first, or carrier-starting, gas-tube VI The circuit I5 is also utilized to energize one terminal of another cathode-circuit loading-resistor R5, the other terminal of which is connected to the cathode-circuit 22 of the second, or relay-energizing, gas-tube V2.

The two grid-terminals of these tubes VI and V2 are connected to their respective cathode-circuits 2| and 22 through capacitors CI and C2, as is known in the art. The two plate-circuits PI and P2 of these two tubes are connected together through a capacitor G3 which assists in firingtransfer. The two cathode-circuit loading-resistors R4 and R5 are respectively shunted by capacitors C4 and C5, which also assist in firingtransfer. The circuit I4, which is connected to an intermediate tap of the cathode-circuit biasing-resistor R3, is also connected to the circuits of the screen grids SC-I and SG2 of the respective gas-tubes VI and V2. The two plate or anode-circuits P! and P2 of the two gas-tubes are connected, respectively, through resistors R6 and R7, to a common conductor 24, which is in turn connected to the positive bus through a resistor R8.

The two alternately firing gas-tubes VI and V2 are supervised by the low-set fault-detector FDI, by having the positive tube-circuit 24 connected to the negative terminal through the 4 normally closed back-contact 25 of the low-set fault-detector FDI.

The circuits of the several relays which are used in my invention are arranged, as far as practicable, after the manner of a schematic diagram or across-the-line diagram. In each case, the main or operating coil of the relay is given a letter-designation or legend, and the same letter-designation or legend is applied to all of the contacts of that relay. The relays and switches are invariably shown in their open or deenergized positions. Arrows are used to symbolically indicate how the various parts of each relay are connected together.

The back-contact 25 of the low-set fault-detector FDI is also used to control the energization of an auxiliary relay K, by having the operating-coil K of this auxiliary relay connected, through a resistor R9, across the FDI back-contact. The auxiliary relay K has a, single backcontact K, which is connected in series with a telemetering key TM, which is indicated by way of illustration of carrier-current control for purposes other than relaying. The auxiliary-relay back-contact K thus acts substantially like a back-contact placed upon the low-set fault-detector FDI, said auxiliary relay K being utilized for supplying this contact in order to avoid mechanically overloading the low-energy fault-detector FDI.

The cathode-circuits 2| and 22 of the respective gas-filled tubes VI and V2 are used as sources of two alternating series of square-topped positive-voltage impulses, for two different purposes. These positive-voltage impulses are the voltagedrops through the respective cathode-circuit loading-ressitors R4 and R5, which have voltagedrops therein when their respective tubes VI and V2 are firing.

The cathode-circuit 2| of the first gas tube VI is used to energize the plate-circuit P3 of 2. ca.- rier-current master-oscillator tube 080, through a radio-frequency choke-coil RFC-I. This occillator-tube OSC serves as carrier-current transmitter for transmitting a succession of bursts of substantially square-topped, or unmodulated, carrier-frequency impulses to the other line-section terminal (not shown), as will be subsequently described. During fault-free conditions of the transmission-system, the gas-tubes VI and V2 are not firing, because of the shortcircuiting' back-contact FDI, and at such times the carrier-current oscillator OSC may be energized through the telemetering key TM, and the back-contact K, which connect the circuit 2| to the positive bus through a resistor RI0.

The transmitter-oscillator CS0 has its screengrid SG3 connected to the plate-supply circuit 2| of said oscillator. The cathode-circuit of the oscillator OSC is the previously-mentioned circuit or conductor I5. The oscillator has a gridcircuit G3, which is connected to the cathodecircuit I5 through a grid-resistor RI The plate-circuit P3 of the oscillator CS0 is connected, through a blocking-capacitor BCI, to an intermediate terminal 21 of a tuned carrierfrequency circuit which determines the carriercurrent frequency of the transmitter. This tuned circuit comprises the conductor 21, a capacitor C6, a conductor 28, a capacitor C1, the cathode-circuit I5, a capacitor C8, the grid-circuit G3, and a variometer LI, the other terminal of which is connected to the starting-point 21 of the tuned circuit.

The conductors 28 and G3 of this tuned circuit are respectively utilized to apply radioor carrier-frequency control-voltages, through blocking-capacitors BCZ and B03 respectively, to the grids of two amplifier-tubes Al and A2. cathodes of the amplifiers Al and A2 are connectedfto the cathode-circuit l5 of the oscillator OSC. The grids of the amplifier tubes Al and A2 are connected, through grid-resistors GRI and GR2, to the negative bus so as to apply a negative bias equal to the drop across the oathode-circuit biasing-resistor R3. The two plates of the amplifiers Al and A2 are connected to the primary-winding terminals of a radio-frequency output-transformer OT. The primary winding of said output-transformer OT has a midpoint tap 30 which is connected to the positive supply-terminal and also to the screen-grids of the two amplifiers Al and A2.

The radio-frequency output-transformer OT has a secondary winding 3|, having one of its terminals grounded, and having two taps 32 and 33. The output-transformer secondary-tap 32 is connected to phase-C of the line I, through a variorneter L2, a conductor 34, and a couplercapacitor CC. The conductor 34 is also grounded through a grounding-coil GC. The secondary tap 33 of the radio-frequency output-transformer OT is utilized to energize the primary winding of a receiver-coupling transformer RCT, through a tuning-capacitor TC. d

The radio-frequency of the tuned receivercircuit (T C, RCT) may,or may not, be different from the radio-frequency of the tunedtransmitter circuit (LI, C6, C1, C8), according to local conditions of the particular transmission-system" in which the apparatus is installed. It is an ob.- jectof my invention to provide a protective-relay system in which the carrier-current frequencies of a substantially constant magnitude, when-- ever the tube is conducting at all, substantially regardless of the voltage applied to the grid-circuit G4, provided thatthis grid-voltage is high enough to cause plate-current to flow.

The receiver-tube REC has its cathode-circuit 3; energized from a tapped point of a potentiometer P04 which is connected between the circuit l5 and the positive bus The receivertube REC has a plate circuit-P4, which is enersized from the positive supply-terminal through a radio-frequency choke-coil RFC-4. In the drawing illustrative of my invention, I

have symbolically shown the telemetering relays 38 in series with the plate-circuit P4, although it should. be understood that, in general, the telemetering relays 38 would be used only at one lineterrninal, while the telemeterinlg key TM would be used. at the other line-terminal. The receiverrelay REC also has a screen-grid circuit SG4 which is connected to the positive terminal (11-).

The

- l5 and the positive supply-terminal The receiver-relay plate-circuit P4 is used t0. apply a restraining voltage to the grid-circuit G5 of a relay-tube RT, through a coupling-capacitor ll--19, a conductor 39, a voltage-doublerwhich is generically indicated at 46, and a grid-circuit resistor R|2. The voltage-doubler 40 consists of an input-resistor R-l3 which is connected to the conductor 39, a capacitor Cl l, which is connected between the circuit 39 and a circuit 4|, a doublecircuit rectifier-valve RV, and an output-resistor or l0ading-resistor R-l4. The loading-resistor R-l4 is connected between the anode-circuit 42 of the right-hand rectifier of the rectifier-valve RV, and a circuit 43 which is connected to the input-resistor R-l3. The anode-circuit 42 also constitutes the input-terminal of the grid-circuit resistor R l2 of the receiver-tube RT. The cathode of the right-hand half of the double-rectifier valve RV is connected to the conductor 4|, while the anode of the left-hand rectifier-circuit of the double valve RV is connected to this same conductor. of the double valve RV is connected to the circuit 43 between the input and output-resistors R-l3 and Rl4. The output-resistor R-l4 of the voltage-doubler is by-passed by a ripplesmoothing radio-frequency by-pass capacitor BPC.

In accordance with my present invention, I provide a delayed-build-up means, whichis essentially a low-pass filter (L and C) shunted by a rectifier 44. This low-pass filter is connected between the cathode-circuit 22 of the second gas-tube V2 and the circuit '43 of the voltagedoubler 40. The filter-inductance L, and the rectifier 44 are connected, in parallel-circuit relation to each other, between thecircuits 22 and 43, with the rectifier 44 in such polarity that it conducts current in the direction from the cir-- cuit 43 to the circuit 22. The filter-capacitor C is connected between the circuits 43 and I5.

The relay-tube RT has its cathode-circuit 45 energized from a tapped point of a potentiometer P05 which is connected between the conductor The plate-circuit P5 of the relay-tube RT is connected through the primary winding of a relay outputtransformer ROT, a conductor 4 a make-contact 41 of the high-set fault-detector FDZ, and thence to the positive terminal The screen-grid circuit 5G5 of the relay-tube RT is also connected to the aforesaid conductor 46.

The relay output-transformer ROT has a secondary winding 48, which is used to energize the operating coil R of a relay R which has a single make-contact 49, which is shown, near the top of the negative supply-terminal as being in the tripping-circuit of the trip-coil TC of the circuit breaker 3, this trip-circuit extending from the negative bus to the positive bus and also including the auxiliary breakercontact 3a.

Before describing the operation of the novel features of my invention, I will first describe the general operation of the carrier-current protective-relay system. When a fault of a predetermined severity occurs on the protected linesection I, one or both of the two fault-detectors FDI and FDZ will pick up. The low-set detector FBI is the more sensitive of the two, and when it responds, it opens its back-contact 25, and thus removes a short circuit from around the two gas tubes VI and V2. The grid-circuit setting of these gas-tubes VI and V2 is such that said tubes are already in readiness tofire, in response The cathode of the left-handrectifier to the alternating voltages which are applied to their respective grids GI and G2.

Whichever one of the two gas tubes VI and V2 has a positive grid voltage applied to it, at the moment of opening of the FDI back-contact 35, will instantly begin firing, developing a certain positive voltage in its cathode-circuit 2! or 22, as the case may be, making said cathode-circuit positive with respect to the conductor [5. During the next half-cycle of the line-current, or output of the secondary winding 6 of the saturating transformer ST, a positive grid-voltage is applied to the other one of the two gas-tubes V l and V2, causing this other tube to fire, putting out the first-firing gas-tube, in the process. The two gas-tubes VI and V2 thus operate as sources of two difierent series of fiat-topped voltage-waves of constant magnitude, one gas tube being respontive to positive line-frequency half-cycles, while the other is responsive to negative line-frequency half-cycles.

Carrier-current is transmitted by the conduct ing or operation of the master-oscillator tube OSC during the flat-topped voltage impulses which are supplied from the cathode-circuit ii of the first gas-tube Vl, thus transmitting a succession of bursts of carrier-current energy, which are applied to the line through the coupling capacitors CC, during line-current half-cycles of one polarity. During the line-current halfcycles of the other polarity, positive or operating-voltage is applied to the grid-circuit G of the relay-tube RT through the cathode-circuit 22 of the second gas-tube V2, the voltage of the circuit 22 being applied to the grid-circuit G5 through my newly added delayed-build-up means (L, C, 44) and the output-resistor R-s4 of the receiver-energized voltage-doubler 48. The operating-voltage, which is applied to the relaytube RT by the circuit 22, tends to cause the flow of plate-current in the relay-tube RT.

If the carrier-frequencies of the transmitter and receiver are identical, the carrier-current impulses which are transmitted from both ends of the protected line-section are received in the receiver-tube REC at each end of the linesection, but if the transmitter and receiver frequencies are difierent, each receiver receives only the impulses which are transmitted from the other line-terminal. The only important re ceived carrier-impulses, at either end, are those which are received from the other terminal, or from the far end of the protected-line section, because the carrier-current impulses, or bursts, or operating-periods, which are transmitted from the relaying station itself, always occur during the half-cycles of the line-current when no operating-voltage is applied to the grid-circuit G5 of the relay-tube RT from the cathode-circuit 22 of the second gas tube V2. At the far end of the protected line-section, however, I the carrier-current energy-impulses or bursts, which are transmitted at line-frequency half-cycle in-- tervals, are transmitted in response to the cathode-circuit 2i of the first gas tube V! in that station, so that, if the in-looking line-current at the far-end station is 180 out of phase with the line-current at the relaying station (as it will be, on short lines of moderate voltage, when there is no fault in the protected line section), then the carrier-current transmitting-periods at the far end will exactly coincide with the operatingvoltage half -cycle periods at the relaying station, and thus they will theoretically block a response of the relay-tube RT.

The received carrier-current energy is applied, in a blocking fashion, to the grid-circuit G5 of the relay-tube RT, through the coupling capacitor C-lll and the voltage-doubler 40, which operates to build up a negative voltage, in the loading-resistor R--l4, which is at least as large as, and opposite in sign to, the positive gridvoltage which is supplied by the cathod-circuit 22 of the second gas tube V2.

The result of the foregoing operations is that the relay-tube RT will become conducting only when there is an internal fault, or a fault within the protected line-section I, in which case the tube will become conducting periodically, in short or long bursts, depending upon the phaserelations between the line-currents at the 0pposite ends of the protected line-section. Troublesome phase-relations may exist between the opposite-end line-currents during throughfault conditions, even in the case of singlefrequency phase-angle relaying-systems, if the line-voltage is particularly high, or if the linesection is particularly long. A high line-voltage may cause charging-currents which can make the total line-current at the sending end or power-source end lead the load-end current by an appreciable phase-angle. Also, if the linesection is unusually long, the propagation-time required for the carrier wave to travel from the load-end to the power end of the protected linesection can amount to an appreciable part of a line-frequenc cycle, giving the efifect of an appreciable line-frequency phase-angle shift. When these two efiects are present concurrently,

my time-delay network LC-44 is usually needed, to prevent faulty operation, even in single-frequency phase-angle relaying-systems.

The alternating-currentcomponentof theplatecurrent of the relay-tube RT is applied to the operating coil of the phase-angle-responsive re lay R, through the relay output-transformer ROT. The contact 48 of the relay R is then utilized to trip the breaker 3.

It will be noted that the carrier-current equipment acts as a pilot-channel connecting the two ends of the protected line-section for the purpose of effecting a determination or comparison of the phase-angle between the two terminal line-currents of the protected line-section.

My newly added low-pass filter (L, C) allows the square-topped operating-voltage impulses, which appear in the circuit 22, to build up only gradually, because the filter will not pass the higher harmonics of the square wave of'the operating voltage. The filter thus delays the buildup of each operating-voltage impulse which is applied to the grid-circuit G5 of the relay-tube RT. This delayed build-up of the operatingvoltage impulses is desirable, as previously explained, in order to match or exceed the delayed build-up of the receiver-responsive restraintvoltage impulses, due to the inability of the tuned receiver-circuits (TC, RCT) and (36,09) to pass these same high harmonics in the received square wave of carrier energy, which is particularly important in cases in which the carrier-current receiver is operating at a diiferent carrier-current frequency than the transmitter.

If the low-pass filter (L, C) were used alone, without the shunt-connected rectifier 44, this filter would also delay the collapse or decay of each of the square-top operating-voltage impulses, which would be undesirable, because it would cause the application of an operatingvoltage to the tube during the first portion of the line-frequency half-cycle during which no operating-voltage was intended to be applied. To correct this condition, the rectifier 44 is connected across the inductance L of the filter, so as to allow the filter-voltage impulses to decay rapidly, by letting the filter-capacitor C discharge through the circuit including the conductor 43, the filter-shunting rectifier 44, the conductor 22, and the cathode-circuit resistor R of the gas-tube V2. For currents flowing in the other direction, the filter-shunting rectifier 44 has a sufficiently high resistance so that it has a negligible effect upon the rate of building-up of the operating-voltage impulses, as applied to the grid-circuit G4 of the relay-tube RT.

It will thus be seen that I have provided a means whereby a phase-comparing carrier-current protective-system may be operated with either a single carrier-current frequency or with diiferent frequencies for the transmitter and the receiver, without the risk of a faulty relay-operation resulting from the failure of the receiver to pass the higher Gil-cycle harmonics during double-frequency operation of the carrier-current protective-relay system.

While I have illustrated my invention, and described its application, in but a single form of embodiment, which has been chosen for illustrative purposes, I wish it to be understood that many changes of addition, substitution or deletion could be made, Without departing from the essential spirit of my invention. I desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language.

I claim as my invention:

1. Terminal equipment for one terminal of a pilot-channel phase-angle relaying-system for an alternating-current line, comprising the combination, with a relay to be controlled, and a pilot-channel means for communicating with another terminal of the protected line-section, of means for deriving an alternating-current line-current quantity which is responsive to a plurality of different line-fault conditions, impulse-producing means for applying a succession of substantially square-topped operating-impulses and a succession of substantially squaretopped pilot-channel-controlling impulses on alternate half-cycles of said derived line-current quantity, circuit-means, including a delayedbuild-up means, for applying said succession of operating-impulses to said relay, said delayedbuild-up means being operative to delay the building-up of the operating-impulses in the relay without substantially delaying the decay thereof, means for delivering said pilot-channelcontrolling impulses to the pilot-channel means,

and receiving-means for applying restrainingimpulses, efiective on said relay, in response to topped transmitter-controlling impulses on al-,

ternate half-cycles of said derived line-current quantity, circuit-means, including a delayedbuild-up means, for applying said succession of operatingdmpulsesto said relay, said delayedbuild-up means being operative to delay the building-up of the operating-impulses in the relay without substantially delaying the decay thereof, means for delivering said transmittercontrolling impulses to the transmitter, and means, responsive to the receiver, for applying restraining-impulses to said relay.

3. The invention as defined in claim 1, characterized by said delayed-build-up means comprising a low-pass filter and a shunt-connected rectifier.

4. The invention as defined in claim 2, characterized by said delayed-buildup means comprising a low-pass filter and a shunt-connected rectifier.

HERBERT W. LENSNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,406,617 Lensner Aug. 27, 1946 2,422,570 Lensner et a1. June 17, 1947 OTHER REFERENCES Geophysics, vol. IV, No. 4, October 1939, pages 284, 285. 

